System and method for providing supercritical steam

ABSTRACT

A system for providing supercritical steam including a first boiler that generates steam via combusting a first fuel, and a second boiler fluidly connected to the first boiler via a conduit which heats the generated steam to supercritical steam temperatures via combusting a second fuel. A first temperature of the conduit may be below a critical corrosion temperature and a second temperature of the conduit is greater than or equal to the critical corrosion temperature. A combined carbon emission rate of the first boiler and the second boiler may be less than a combined carbon emission rate of generating and heating the steam to supercritical steam temperatures using boilers that only combust the first fuel. The first boiler may be fluidly connected to a heat exchanger that heats the generated steam to a supercritical steam temperature via a flue gas produced by a gas turbine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.:15/340,670 filed on Nov. 1, 2016, which is herein incorporated byreference in its entirety.

BACKGROUND Technical Field

Embodiments of the invention relate generally to power plant technologyand, more specifically, to a system and method for providingsupercritical steam.

Discussion of Art

Boilers are devices that combust a fuel, such as petroleum basedproducts and/or coals, in a combustion chamber to generate heat. Manypower plants use boilers to generate steam which in turn is used toproduce electricity via a steam turbine generator. The ratio ofelectricity produced by a power plant per a given amount of fuel isknown as the plant's efficiency. The efficiency of a power plant can beincreased by increasing the temperature and/or pressure of the generatedsteam that powers the steam turbine generator.

Accordingly, the boilers of many modern coal power plants generate steamin the supercritical steam range, e.g., steam having a temperaturegreater than or equal to 565° C. The boilers of many modern oil-basedpower plants, however, are limited in their ability to sustaingeneration of supercritical steam due to the tendency of contaminantsproduced by combusting petroleum based oils to become corrosive at orabove the surface temperatures of conduits that contain supercriticalsteam. Typically, when such contaminants come into contact with conduitscontaining supercritical steam, the contaminants may slag, foul,corrode, and/or damage the conduit. Generally, the lower thegrade/quality of the petroleum based oil being fired/combusted in aboiler, the more contaminants produced, and the greater the resultingcorrosion to the conduits.

Many refiners are increasing the production of high-grade petroleumproducts which has resulted in an increase in the amount of low-gradepetroleum based oil by-products, such as Oil Heavy Residue (“OHR”). Therecent relative abundance of such low-grade petroleum based oils nowmakes them economical for use as fuels in power plants. Therefore, manymodern oil-based power plants are now designed to fire low-gradepetroleum based oils. As previously stated, however, the nature of thecontaminants produced by combusting low-grade petroleum based oils tobecome corrosive at or above the surface temperatures of conduits thatcontain supercritical steam hinders the efficiency of modern oil-basedpower plants.

Moreover, combustion of low-grade petroleum based oils tends to producehigh amounts of Carbon Dioxide (“CO₂”). Due to increased concern thatCO₂ may be contributing to global warming, it is now desirable to reducethe CO₂ emissions of power plants.

What is needed, therefore, is a system and method for providingsupercritical steam which inhibits the corrosion resulting from thecontaminants produced by combusting petroleum based oils, and/or whichemits less CO₂ than existing oil based power plants.

BRIEF DESCRIPTION

In an embodiment, a system for providing supercritical steam isprovided. The system includes a first boiler and a second boiler. Thefirst boiler generates steam via combusting a first fuel. The secondboiler is fluidly connected to the first boiler via a conduit such thatthe generated steam flows from the first boiler to the second boilerwhich heats the generated steam to a supercritical steam temperature viacombusting a second fuel that is different from the first fuel. A firsttemperature of the conduit is below a critical corrosion temperature atwhich contaminants produced by combusting the first fuel corrode theconduit and a second temperature of the conduit is greater than or equalto the critical corrosion temperature.

In another embodiment, a method for providing supercritical steam isprovided. The method includes: generating steam via combusting a firstfuel in a first boiler fluidly connected to a second boiler via aconduit such that the generated steam flows from the first boiler to thesecond boiler; and heating the generated steam to a supercritical steamtemperature via combusting a second fuel that is different from thefirst fuel in the second boiler. In such embodiments, a firsttemperature of the conduit is below a critical corrosion temperature atwhich contaminants produced by combusting the first fuel corrode theconduit and a second temperature of the conduit is greater than or equalto the critical corrosion temperature.

In yet another embodiment, a downstream boiler for providingsupercritical steam is provided. The downstream boiler includes acombustion chamber and a steam conduit. The combustion chamber isconfigured to generate heat by combusting a first fuel. The steamconduit is in heating-contact with the combustion chamber and has aninlet and an outlet. The inlet is configured to fluidly connect to anupstream boiler that generates steam by combusting a second fuel that isdifferent from the first fuel. The outlet is configured to fluidlyconnect to a steam turbine generator. When the inlet receives steamgenerated by the upstream boiler, the combustion chamber heats thereceived steam in the conduit to a supercritical steam temperature viacombusting the first fuel such that a temperature of the steam conduitis greater than or equal to a critical corrosion temperature at whichcontaminants produced by combusting the second fuel corrode the steamconduit.

In yet another embodiment, a system for providing supercritical steam isprovided. The system includes a first boiler and a second boiler. Thefirst boiler generates steam via combusting a first fuel. The secondboiler is fluidly connected to the first boiler via a conduit such thatthe generated steam flows from the first boiler to the second boilerwhich heats the generated steam to a supercritical steam temperature viacombusting a second fuel that is different from the first fuel. In suchembodiments, a combined carbon emission rate of the first boiler and thesecond boiler is less than a combined carbon emission rate of generatingand heating the steam to a supercritical steam temperature using one ormore boilers that only combust the first fuel.

In yet another embodiment, a method for providing supercritical steam isprovided. The method includes: generating steam via combusting a firstfuel in a first boiler fluidly connected to a second boiler via aconduit such that the generated steam flows from the first boiler to thesecond boiler; and heating the generated steam to a supercritical steamtemperature via combusting a second fuel that is different from thefirst fuel in the second boiler. In such embodiments, a combined carbonemission rate of the first boiler and the second boiler is less than acombined carbon emission rate of generating and heating the steam to asupercritical steam temperature using one or more boilers that onlycombust the first fuel.

In yet another embodiment, a downstream boiler is provided. Thedownstream boiler includes a combustion chamber and a steam conduit. Thecombustion chamber is configured to combust a first fuel. The steamconduit is in heating-contact with the combustion chamber and has aninlet and an outlet. The inlet is configured to fluidly connect to anupstream boiler that generates steam by combusting a second fuel that isdifferent from the first fuel. The outlet is configured to fluidlyconnect to a steam turbine generator. In such embodiments, a combinedcarbon emission rate of the downstream boiler and the upstream boiler isless than a combined carbon emission rate of one or more boilers thatonly combust the second fuel.

In yet another embodiment, a system for providing supercritical steam isprovided. The system includes a primary boiler that generates steam viacombusting a first fuel; a gas turbine that produces a flue gas viacombusting a second fuel that is different from the first fuel; and aheat exchanger fluidly connected to the primary boiler and to the gasturbine via a first conduit and a second conduit, respectively. Thegenerated steam and the flue gas flow from the primary boiler and thegas turbine via the first conduit and the second conduit, respectively,to the heat exchanger which heats the generated steam via the flue gasto a supercritical steam temperature.

In yet another embodiment, a method for providing supercritical steam isprovided. The method includes: generating steam via combusting a firstfuel in a primary boiler fluidly connected to a heat exchanger via afirst conduit such that the generated steam flows to the heat exchangerfrom the primary boiler via the first conduit; and heating the generatedsteam to a supercritical steam temperature via a flue gas produced bycombusting a second fuel in a gas turbine fluidly connected to the heatexchanger via a second conduit such that the flue gas flows to the heatexchanger via the second conduit, the second fuel being different fromthe first fuel.

DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 is a block diagram of a system for providing supercritical steamin accordance with an embodiment of the invention;

FIG. 2 is a flow chart depicting a method for providing supercriticalsteam via the system of FIG. 1 in accordance with an embodiment of theinvention;

FIG. 3 is an additional diagram of the system of FIG. 1, wherein thesystem includes an oxy-fired boiler;

FIG. 4 is an additional diagram of the system of FIG. 1, wherein thesystem includes a gas turbine in accordance with an embodiment of theinvention; and

FIG. 5 is a flow chart depicting a method for providing supercriticalsteam via the system of FIG. 4 in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

Reference will be made below in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference characters usedthroughout the drawings refer to the same or like parts, withoutduplicative description.

As used herein, the terms “substantially,” “generally,” and “about”indicate conditions within reasonably achievable manufacturing andassembly tolerances, relative to ideal desired conditions suitable forachieving the functional purpose of a component or assembly. As usedherein, “electrically coupled,” “electrically connected,” and“electrical communication” mean that the referenced elements aredirectly or indirectly connected such that an electrical current mayflow from one to the other. The connection may include a directconductive connection, i.e., without an intervening capacitive,inductive or active element, an inductive connection, a capacitiveconnection, and/or any other suitable electrical connection. Interveningcomponents may be present. As also used herein, the term “fluidlyconnected” means that the referenced elements are connected such that afluid (to include a liquid, gas, and/or plasma) may flow from one to theother. Accordingly, the terms “upstream” and “downstream,” as usedherein, describe the position of the referenced elements with respect toa flow path of a fluid flowing between and/or near the referencedelements. Additionally, as used herein, the term “fill” includes bothfully and partially filling a containing object with a filling object.As used herein, the term “heating-contact” means that the referencedobjects are in proximity of one another such that heat/thermal energycan transfer between them. As used herein, the terms “critical corrosiontemperature” and “critical corrosive temperature” refer to a temperatureat which contaminants produced via combusting a fuel become corrosive soas to slag, foul, corrode, and/or damage various components of a boilerbeyond an acceptable level. As used herein, the terms “corrode” and“corrosive” mean capable of causing damage to a material via chemicalmeans, e.g., oxidation and/or acid-base reactions. For example, whensuch a contaminant comes into contact with a surface of a conduit thatis above the critical corrosive temperature of the contaminant, thecontaminant may melt and stick to the surface of the conduit such thatthe conduit becomes degraded/damaged, e.g., the melted contaminant mayfoul and/or “eat away” at the conduit. As used herein, the terms“supercritical steam” and “supercritical steam temperature” refer tosteam and its corresponding temperature after having been heated for asecond time by a second heating source, e.g., a second boiler to atemperature higher than that to which the steam was previously heated toby a first heating source, e.g., a first boiler. As also used herein theterm “combined carbon emissions” refers to the total amount of CO₂generated by one or more boilers/combustion chambers. Accordingly, theterm “combined carbon emission rate,” as used herein, refers to thecombined amount of CO₂ generated by one or more boilers/combustionchambers to produce a given amount of electricity and/or power.

Further, while the embodiments disclosed herein are described withrespect to oil fired boilers that generate supercritical steam, it is tobe understood that embodiments of the present invention are equallyapplicable to any device and/or process in which a conduit and/or otherstructural element that is exposed to contaminants produced bycombusting a fuel is required to be heated to a temperature higher thana critical corrosive temperature of the contaminants, and/or processeswherein it is desirable to reduce CO₂ emissions.

Accordingly, referring to FIG. 1, a system 10 for providingsupercritical steam is provided. The system 10 includes a first boiler12 and a second boiler 14. The system 10 may further include a steamturbine generator 16, an air preheater (“APH”) 18, an electrostaticprecipitator (“ESP”) and/or fabric filter (“FF”) 20, a flue gasdesulfurization unit (“FGD”) 22, a secondary air source 24, an exhauststack 26, one or more conduits 28-42 which may have one or more checkvalves 44, 46, and/or a controller 48.

The first boiler 12 includes a combustion chamber 50 which generatesheat, e.g., thermal energy, by combusting a first fuel 52. The firstboiler 12 may further include a fuel inlet 54, and an exhaust outlet 56.The fuel inlet 54 allows the first fuel 52 to flow, via conduit 40, tothe combustion chamber 50. The exhaust outlet 56 vents a first flue gasproduced from combusting the first fuel 52 in the combustion chamber 50.The combustion chamber 50 may be in heating-contact with conduit 28(hereinafter referred to as steam conduit 28) which contains a workingmedium, e.g., water and/or another appropriate medium capable of storingthermal energy. In embodiments, the exhaust port 56 may be fluidlyconnected to the exhaust stack 26, via conduit 34 (hereinafter referredto as exhaust conduit 34), such that the vented first flue gas flowsfrom the combustion chamber 50 to the exhaust stack 26. As shown in FIG.1, the APH 18, ESP/FF 20, and FGD 22 may be disposed in/along theexhaust conduit 34 such that APH 18, ESP/FF 20, and FGD 22 treat and/orclean the first flue gas prior to being expelled into the atmosphere bythe exhaust stack 26. In embodiments, the first fuel 52 may be an oil toinclude Oil Heavy Residue (“OHR”) and/or Heavy Fuel Oil (“HFO”). As willbe appreciated, in embodiments, OHR may be a blend of low gradepetroleum fuels and/or solid fuels, e.g., coal and/or petroleum coke,which may contain a high amount of metals, e.g., V, Ni, Na, etc., and/orsulfur. For example, in some embodiments, the metal content of the firstfuel 52 may be 0 to 1000 ppm and the sulfur content may be between 0 and15% by weight.

The second boiler 14 includes a combustion chamber 58 which generatesheat, e.g., thermal energy, by combusting a second fuel 60. The secondboiler 14 may further include a fuel inlet 62 and an exhaust outlet 64.The fuel inlet 62 allows the second fuel 60 to flow, via conduit 42, tothe combustion chamber 58. The exhaust outlet 64 vents a second flue gasproduced from combusting the second fuel 60 in the combustion chamber58. In embodiments, the exhaust outlet 64 of the second boiler 14 may befluidly connected, via conduit 32 (hereinafter referred to as flue gasconduit 32), such that the vented second flue gas flows from thecombustion chamber 58 of the second boiler 14 to the first boiler 12.For example, in such embodiments, the flue gas generated by the secondboiler 14 may be in heating-contact with an economizer, a feed waterheating line, and/or an air pre-heater, e.g., APH 18, of the firstboiler 12. In embodiments, the flue gas conduit 32 may be fluidlyconnected to the first boiler 12 at a convective bypass 70 of the firstboiler 12.

As shown in FIG. 1, the combustion chamber 58 may also be inheating-contact with the steam conduit 28. The steam conduit 28 includesan inlet 66 and an outlet 68 configured to fluidly connect to the firstboiler 12 and to the steam turbine generator 16, respectively. As is tobe appreciated, in embodiments, the steam conduit 28 may be a singleconduit or may include segments fluidly connected to one another. Forexample, in embodiments, conduit 30, (hereinafter referred to assupercritical steam conduit 30), may form part of the steam conduit 28that connects the second boiler 14 to the steam turbine generator 16. Inembodiments, the supercritical steam conduit 30 may be configured, e.g.,the walls of the supercritical steam conduit 30 may be relatively thick,to contain supercritical steam. As is to be appreciated, in embodiments,the steam conduit 28 may form part of the second boiler 14 and/orotherwise be disposed in the second boiler 14.

In embodiments, the first 12 and/or the second 14 boilers may be fluidlyconnected, via conduit 36 (hereinafter referred to as the secondary airconduit 36), to the secondary air source 24 which may supply hot air tothe combustion chambers 50 and 58 to improve the efficiency of the first12 and/or the second 14 boilers, respectively, e.g., the secondary airsource 24 may be common between the first 12 and the second 14 boilers.In other embodiments, however, the first 12 and the second 14 boilersmay utilize independent secondary air sources. As shown in FIG. 1, theAPH 18 may be disposed in the secondary air conduit 36.

The controller 48 may include at least one processor/CPU 72 and a memorydevice 74 that stores a heating program/application. The controller 48may be disposed in the system 10 such that the controller 48 is inelectronic communication with the various components, to include thefirst 12 and the second boilers 14.

Turning now to FIG. 2, a method 76 for providing supercritical steam viathe system 10 is shown. As is to be appreciated, in embodiments, aheating application stored in the memory device 74 may be loaded intothe at least one processor/CPU 72 such that the controller 48 is adaptedby the heating application to perform all, or part, of method 76. Thus,in embodiments in accordance with the method 76, the first boiler 12generates 78 steam via combusting the first fuel 52 such that a firsttemperature of the conduit 28 that contains the steam is below acritical corrosion temperature at which contaminants produced bycombusting the first fuel 52 corrode the conduit 28. In embodiments, thefirst temperature of the conduit 28 may be the temperature of thesections of the conduit 28 that are exposed to the contaminants producedvia combusting the first fuel 52. For example, in embodiments, thecontaminants produced by combusting the first fuel 52 may have acritical corrosion temperature of 600° C. Accordingly, the first boiler12 may be configured to limit the first temperature of the conduit 28 toa temperature lower than 600° C. by limiting the temperature of thesteam contained in the sections of the conduit 28 that are exposed tothe contaminants produced via combusting the first fuel 52 to 540° C.While the embodiments disclosed herein limit the first temperature ofthe conduit 28 by limiting the temperature of the steam contained withinthe sections the conduit 28 that are exposed to the contaminantsproduced via combusting the first fuel 52, it is to be understood thatother embodiments may limit the first temperature of the conduit 28 bylimiting the firing temperature of the first fuel 52.

The generated steam then flows, via the steam conduit 28, to the secondboiler 14 where the steam is heated 80 to a supercritical steamtemperature via combusting the second fuel 60 in the combustion chamber58 such that a second temperature of the conduit 28 is greater than orequal to the critical corrosion temperature of the first fuel 52. Thesecond temperature of the conduit 28 may be the temperature of thesections of the conduit 28 that are not exposed to the contaminantsproduced via combusting the first fuel 52. In embodiments, the secondtemperature of the conduit 28 may be between about 565° C.-700° C. Inembodiments, the second temperature of the conduit 28 may be between630° C.-670° C. which allows the contained steam to reach asupercritical steam temperature at and/or between 600° C.-620° C. Inembodiments, the supercritical steam may have a temperature between 594°C.-625° C. In other embodiments, the supercritical steam may have atemperature higher than 625° C. and/or lower than 594° C. For example,in some embodiments, the supercritical steam may have a temperature onthe order of 565° C. or greater than or equal to 700° C. It is to beunderstood, however, that the aforementioned ranges are merely exemplaryand are not intended to be limiting.

Thus, as is to be appreciated, in embodiments, the first boiler 12provides the majority of the steam duty by heating the working medium toa superheated state, and the second boiler 14 provides the remainingsteam duty by heating the superheated working medium to a supercriticalsteam temperature.

It is to be understood that, in embodiments, the second fuel 60 is of ahigher grade and/or “cleaner” than the first fuel 52. The terms “clean”and “dirty,” as used herein with respect to fuels, refer to the level ofCO₂ and/or corrosive contaminants produced via combusting the fuels,wherein combustion of an amount of a clean fuel produces less CO₂ and/orless corrosive contaminants that does combustion of an equal amount of adirty fuel. For example, in embodiments, the second fuel 60 may be agas, a blend of various liquid fuels, e.g., diesel, kerosene, and/orcrude oil, and may additionally include blended solid fuels, e.g., coal,lignite, and/or biomass. In some embodiments, the second fuel 60 mayhave a low metal, e.g., below 10 ppm, and/or sulfur content. As such,combustion of the second fuel 60 may produce fewer contaminants thancombustion of the first fuel 52. Thus, the second temperature of theconduit 28 may be higher than the first temperature of the conduit 28without an increase in the risk of corrosion to the conduit 28.

The supercritical steam then flows, via the supercritical steam conduit30, to the steam turbine generator 16 which consumes the supercriticalsteam to produce 82 power. For example, in embodiments, the steamturbine generator 16 may produce electrical power as part of anoil-based electrical power generation plant/system.

Continuing, in embodiments, the second boiler 14 may further include areheat inlet 83 that is fluidly connected to the steam turbine generator16, via conduit 38 (hereinafter referred to as reheat-conduit 38), suchthat the second boiler 14 forms part of a reheat-cycle-circuit for thesteam turbine generator 16, e.g., the second boiler 14 provides thereheat duty. In such embodiments, the second boiler 14 may reheat 84steam previously consumed by the steam turbine generator 16 and return,via the supercritical steam conduit 30, the reheated steam back to thesteam turbine generator 16. While the embodiments shown in the providedfigures depict the second boiler 14 returning the reheated steam back tothe steam turbine generator 16 via the supercritical steam conduit 30,it is to be appreciated that in other embodiments the second boiler 14may return the reheated steam back to the steam turbine generator 16 viaother conduits/flow paths which may exists between the second boiler 14and the steam turbine generator 16. For example, in embodiments, conduit38 may extend through the second boiler 14 to the steam turbinegenerator 16.

Additionally, while FIG. 1 shows an embodiment of the system 10 in whichthe first boiler 12 is an air-fired boiler, it is to be understood thatin other embodiments the first boiler 12 may be an oxy-fired boiler.Accordingly, as shown in FIG. 3, in such embodiments, the system 10 mayfurther include a gas processing unit (“GPU”) 86 and an oxygen source88. The GPU 86 may be disposed in the exhaust conduit 34 and thesecondary air conduit 36 as illustrated in FIG. 3. In such embodiments,oxygen may flow, via the secondary air conduit 36, from the oxygensource 88 to the combustion chambers 50 and 58 of the first 12 and thesecond 14 boilers, respectively, e.g., the oxygen source 88 may becommon between the first 12 and the second 14 boilers. Similarly, inembodiments, the second boiler 14 may be an air fired or an oxy-firedboiler. Further, in embodiments, the first 12 and the second 14 boilersmay be connected to independent oxygen sources.

Moving now to FIG. 4, in embodiments, the system 10, may include a gasturbine 92 fluidly connected to a heat exchanger 94 via conduit 96which, as shown, may be incorporated into the second/secondary boiler14. In such embodiments, the gas turbine 92 generates power, e.g.,electrical power, by combusting a fuel, which in embodiments may be thesecond fuel 60, to produce a flue gas that flows from the gas turbine 92to the heat exchanger 94 via conduit 96. The heat exchanger 94 is alsofluidly connected to the first/primary boiler 12, via conduit 28, suchthat the generated steam flows from the primary boiler 12 to the heatexchanger 94 which heats the generated steam via the flue gas from thegas turbine 92. In embodiments, the heat exchanger 94 may heat thegenerated steam to a supercritical steam temperature prior to being sentfor consumption by the steam turbine generator 16. In embodiments, acombined carbon emission rate of the primary boiler 12 and the gasturbine 92 may be less than a combined carbon emission rate ofgenerating and heating the steam to a supercritical steam temperatureusing boilers that only combust/burn the first fuel 52. As also shown inFIG. 4, in embodiments, the flue gas from the gas turbine 92 may also beused to heat the steam in reheat-conduit 38.

As further shown in FIG. 4, in embodiments, a first damper/valve 98 maybe disposed upstream of the heat exchanger 94 within conduit 96 whichallows the flue gas from the gas turbine 92 to be diverted away from theheat exchanger 94 for emission into the atmosphere via an exhaust stack100. Additionally, in embodiments, conduit 96 may be fluidly connectedto a second damper/valve 102 disposed downstream of the heat exchanger94 that allows the flue gas produced by the gas turbine 92 to bedirected to: the stack 26 for emission into the atmosphere; a point justupstream of the ESP/FF 20; and/or conduit 36 such that the flue gasenters combustion chambers 50 and/or 58 to improve the efficiency of thefirst/primary 12 and/or the second/secondary 14 boilers.

As will be appreciated, in embodiments, the gas turbine 92 may have afaster startup procedure time, i.e., the amount of time that it takesfrom starting the gas turbine 92 until power, e.g., electrical power,can be generated, than the startup procedure time for the primary 12and/or the secondary 14 boilers, i.e., the amount of time it takes fromstarting the primary 12 and/or the secondary 14 boilers until power,e.g., electrical power can be generated. In such embodiments, the gasturbine 92 may provide for an encompassing power plant to generate powerfaster than some traditional power plants that rely on boilers for thegeneration of steam. In particular, by diverting the flue gas out theexhaust stack 100, the first damper 98 provides for the gas turbine 92to be utilized for power generation prior to the start of combustion inthe first 12 and/or second 14 boilers.

For example, shown in FIG. 5 is another method 104 for providingsupercritical steam via the system 10. In embodiments, the heatingapplication stored in the memory device 74 may be loaded into the atleast one processor/CPU 72 such that the controller 48 is adapted by theheating application to perform all, or part, of method 104. As shown inFIG. 5, in embodiments, the gas turbine 92 may be used to generate 106power prior to generating 108 steam via the primary 12 and/or thesecondary 14 boilers, wherein the damper 98 diverts the flue gas withinconduit 96 out the exhaust stack 100. Once the primary 12 and/or thesecondary 14 boilers are generating 108 steam, or just prior togenerating 108 steam, the damper 98 may be adjusted such that the fluegas is allowed to flow through conduit 96 to the heat exchanger 94 suchthat the heat exchanger 94 heats 110 the generated steam to asupercritical temperature which is then consumed by the steam turbine 16to produce 112 power, e.g., electrical power.

Further, in embodiments, the gas turbine 92 may be used to generatepower while the primary 12 and/or the secondary 14 boilers are stillbeing constructed and/or while the primary 12 and/or the secondary 14boilers are shut down for maintenance. Similarly, in embodiments, theprimary 12 and the secondary 14 boilers may continue to generate powervia steam turbine 16 while the gas turbine 92 is shutdown.

As will be further appreciated, while embodiments herein depict thesystem 10 as including both the gas turbine 92 and the secondary boiler14, it will be understood that other embodiments may include the gasturbine 92 without the secondary boiler 14, i.e., the gas turbine 92 insome embodiments may stand in place of the secondary boiler 14.

Returning back to FIG. 1, it is also to be understood that the system 10may include the necessary electronics, software, memory, storage,databases, firmware, logic/state machines, microprocessors,communication links, displays or other visual or audio user interfaces,printing devices, and any other input/output interfaces to perform thefunctions described herein and/or to achieve the results describedherein. For example, as previously mentioned, the system 10 may includeat least one processor 72, and system memory 74, which may includerandom access memory (RAM) and read-only memory (ROM). The system 10 mayfurther include an input/output controller, and one or more data storagestructures. All of these latter elements may be in communication withthe at least one processor 72 to facilitate the operation of the system10 as discussed above. Suitable computer program code may be providedfor executing numerous functions, including those discussed above inconnection with the system 10 and methods 76 and 104 disclosed herein.The computer program code may also include program elements such as anoperating system, a database management system and “device drivers” thatallow the system 10, to interface with computer peripheral devices,e.g., sensors, a video display, a keyboard, a computer mouse, etc.

The at least one processor 72 of the system 10 may include one or moreconventional microprocessors and one or more supplementary co-processorssuch as math co-processors or the like. Elements in communication witheach other need not be continually signaling or transmitting to eachother. On the contrary, such elements may transmit to each other asnecessary, may refrain from exchanging data at certain times, and maycause several steps to be performed to establish a communication linktherebetween.

The data storage structures such as memory discussed herein may includean appropriate combination of magnetic, optical and/or semiconductormemory, and may include, for example, RAM, ROM, flash drive, an opticaldisc such as a compact disc and/or a hard disk or drive. The datastorage structures may store, for example, information required by thesystem 10 and/or one or more programs, e.g., computer program code suchas the heating application and/or other computer program product,adapted to direct the system 10. The programs may be stored, forexample, in a compressed, an uncompiled and/or an encrypted format, andmay include computer program code. The instructions of the computerprogram code may be read into a main memory of a processor from acomputer-readable medium. While execution of sequences of instructionsin the program causes the processor to perform the process stepsdescribed herein, hard-wired circuitry may be used in place of, or incombination with, software instructions for implementation of theprocesses of the present invention. Thus, embodiments of the presentinvention are not limited to any specific combination of hardware andsoftware.

The program may also be implemented in programmable hardware devicessuch as field programmable gate arrays, programmable array logic,programmable logic devices or the like. Programs may also be implementedin software for execution by various types of computer processors. Aprogram of executable code may, for instance, includes one or morephysical or logical blocks of computer instructions, which may, forinstance, be organized as an object, procedure, process or function.Nevertheless, the executables of an identified program need not bephysically located together, but may include separate instructionsstored in different locations which, when joined logically together,form the program and achieve the stated purpose for the programs such aspreserving privacy by executing the plurality of random operations. Inan embodiment, an application of executable code may be a compilation ofmany instructions, and may even be distributed over several differentcode partitions or segments, among different programs, and acrossseveral devices.

The term “computer-readable medium” as used herein refers to any mediumthat provides or participates in providing instructions to at least oneprocessor 72 of the system 10 (or any other processor of a devicedescribed herein) for execution. Such a medium may take many forms,including but not limited to, non-volatile media and volatile media.Non-volatile media include, for example, optical, magnetic, oropto-magnetic disks, such as memory. Volatile media include dynamicrandom access memory (DRAM), which typically constitutes the mainmemory. Common forms of computer-readable media include, for example, afloppy disk, a flexible disk, hard disk, magnetic tape, any othermagnetic medium, a CD-ROM, DVD, any other optical medium, a RAM, a PROM,an EPROM or EEPROM (electronically erasable programmable read-onlymemory), a FLASH-EEPROM, any other memory chip or cartridge, or anyother medium from which a computer can read.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to at least one processorfor execution. For example, the instructions may initially be borne on amagnetic disk of a remote computer (not shown). The remote computer canload the instructions into its dynamic memory and send the instructionsover an Ethernet connection, cable line, or telephone line using amodem. A communications device local to a computing device, e.g., aserver, can receive the data on the respective communications line andplace the data on a system bus for at least one processor. The systembus carries the data to main memory, from which the at least oneprocessor retrieves and executes the instructions. The instructionsreceived by main memory may optionally be stored in memory either beforeor after execution by the at least one processor. In addition,instructions may be received via a communication port as electrical,electromagnetic or optical signals, which are exemplary forms ofwireless communications or data streams that carry various types ofinformation.

It is further to be understood that the above description is intended tobe illustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. Additionally, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope.

For example, in an embodiment, a system for providing supercriticalsteam is provided. The system includes a first boiler and a secondboiler. The first boiler generates steam via combusting a first fuel.The second boiler is fluidly connected to the first boiler via a conduitsuch that the generated steam flows from the first boiler to the secondboiler which heats the generated steam to a supercritical steamtemperature via combusting a second fuel that is different from thefirst fuel. A first temperature of the conduit is below a criticalcorrosion temperature at which contaminants produced by combusting thefirst fuel corrode the conduit and a second temperature of the conduitis greater than or equal to the critical corrosion temperature. Incertain embodiments, the first fuel is at least one of a heavy oilresidue, a heavy fuel oil, and a solid fuel. In certain embodiments, atleast one of the first boiler and the second boiler is an air-firedboiler or an oxy-fired boiler. In certain embodiments, the second fuelis a gas or a combination of a gas blended with at least one of a liquidfuel or a solid fuel. In certain embodiments, the first boiler and thesecond boiler are each further fluidly connected to a common air source.In certain embodiments, combustion of the second fuel by the secondboiler produces a flue gas, and the second boiler is further fluidlyconnected to the first boiler such that the flue gas flows from thesecond boiler to the first boiler. In certain embodiments, the systemfurther includes a steam turbine generator fluidly connected to thesecond boiler such that the supercritical steam flows from the secondboiler to the steam turbine generator which consumes the supercriticalsteam to produce power. In certain embodiments, the second boiler formspart of a reheat-cycle-circuit for the steam turbine generator.

Other embodiments provide for a method for providing supercriticalsteam. The method includes: generating steam via combusting a first fuelin a first boiler fluidly connected to a second boiler via a conduitsuch that the generated steam flows from the first boiler to the secondboiler; and heating the generated steam to a supercritical steamtemperature via combusting a second fuel that is different from thefirst fuel in the second boiler. In such embodiments, a firsttemperature of the conduit is below a critical corrosion temperature atwhich contaminants produced by combusting the first fuel corrode theconduit and a second temperature of the conduit is greater than or equalto the critical corrosion temperature. In certain embodiments, the firstfuel is at least one of a heavy oil residue, a heavy fuel oil, and asolid fuel. In certain embodiments, at least one of the first boiler andthe second boiler is an air-fired boiler or an oxy-fired boiler. Incertain embodiments, the second fuel is a gas or a combination of a gasblended with at least one of a liquid fuel or a solid fuel. In certainembodiments, the method further includes producing power via a steamturbine generator that consumes the supercritical steam, the steamturbine generator fluidly connected to the second boiler such that thesupercritical steam flows to the steam turbine generator from the secondboiler. In certain embodiments, the method further includes reheating,via the second boiler, steam previously consumed by the steam turbinegenerator.

Yet still other embodiments provide for a downstream boiler forproviding supercritical steam. The downstream boiler includes acombustion chamber and a steam conduit. The combustion chamber isconfigured to generate heat by combusting a first fuel. The steamconduit is in heating-contact with the combustion chamber and has aninlet and an outlet. The inlet is configured to fluidly connect to anupstream boiler that generates steam by combusting a second fuel that isdifferent from the first fuel. The outlet is configured to fluidlyconnect to a steam turbine generator. When the inlet receives steamgenerated by the upstream boiler, the combustion chamber heats thereceived steam in the conduit to a supercritical steam temperature viacombusting the first fuel such that a temperature of the steam conduitis greater than or equal to a critical corrosion temperature at whichcontaminants produced by combusting the second fuel corrode the steamconduit. In certain embodiments, the first fuel is a gas or acombination of a gas blended with at least one of a liquid fuel or asolid fuel; and the second fuel is at least one of a heavy oil residue,a heavy fuel oil, and a solid fuel. In certain embodiments, thecombustion chamber is configured to be fluidly connected to a common airsource that is also fluidly connected to the upstream boiler. In certainembodiments, the downstream boiler further includes a flue gas conduitthat fluidly connects the combustion chamber to the upstream boiler suchthat a flue gas produced via combustion of the first fuel is broughtinto heating-contact with an economizer of the upstream boiler or a feedwater line of the upstream boiler. In certain embodiments, thedownstream boiler further includes a reheat steam inlet that isconfigured to receive steam from the steam turbine generator as part ofa reheat-cycle for the steam turbine generator.

Yet still other embodiments provide for a system for providingsupercritical steam. The system includes a first boiler and a secondboiler. The first boiler generates steam via combusting a first fuel.The second boiler is fluidly connected to the first boiler via a conduitsuch that the generated steam flows from the first boiler to the secondboiler which heats the generated steam to a supercritical steamtemperature via combusting a second fuel that is different from thefirst fuel. In such embodiments, a combined carbon emission rate of thefirst boiler and the second boiler is less than a combined carbonemission rate of generating and heating the steam to a supercriticalsteam temperature using one or more boilers that only combust the firstfuel. In certain embodiments, the first fuel is at least one of a heavyoil residue, a heavy fuel oil, and a solid fuel. In certain embodiments,at least one of the first boiler and the second boiler is an air-firedboiler or an oxy-fired boiler. In certain embodiments, the second fuelis a gas or a combination of a gas blended with at least one of a liquidfuel or a solid fuel. In certain embodiments, the first boiler and thesecond boiler are each further fluidly connected to a common air source.In certain embodiments, combustion of the second fuel by the secondboiler produces a flue gas, and the second boiler is further fluidlyconnected to the first boiler such that the flue gas flows from thesecond boiler to the first boiler. In certain embodiments, the systemfurther includes a steam turbine generator fluidly connected to thesecond boiler such that the supercritical steam flows from the secondboiler to the steam turbine generator which consumes the supercriticalsteam to produce power.

Yet still other embodiments provide for a method for providingsupercritical steam. The method includes: generating steam viacombusting a first fuel in a first boiler fluidly connected to a secondboiler via a conduit such that the generated steam flows from the firstboiler to the second boiler; and heating the generated steam to asupercritical steam temperature via combusting a second fuel that isdifferent from the first fuel in the second boiler. In such embodiments,a combined carbon emission rate of the first boiler and the secondboiler is less than a combined carbon emission rate of generating andheating the steam to a supercritical steam temperature using one or moreboilers that only combust the first fuel. In certain embodiments, themethod further includes producing power via a steam turbine generatorthat consumes the supercritical steam, the steam turbine generatorfluidly connected to the second boiler such that the supercritical steamflows to the steam turbine generator from the second boiler. In certainembodiments, the method further includes reheating, via the secondboiler, steam previously consumed by the steam turbine generator.

Yet still other embodiments provide a downstream boiler. The downstreamboiler includes a combustion chamber and a steam conduit. The combustionchamber is configured to combust a first fuel. The steam conduit is inheating-contact with the combustion chamber and has an inlet and anoutlet. The inlet is configured to fluidly connect to an upstream boilerthat generates steam by combusting a second fuel that is different fromthe first fuel. The outlet is configured to fluidly connect to a steamturbine generator. In such embodiments, a combined carbon emission rateof the downstream boiler and the upstream boiler is less than a combinedcarbon emission rate of one or more boilers that only combust the secondfuel.

Yet still other embodiments provide for a system for providingsupercritical steam. The system includes a primary boiler that generatessteam via combusting a first fuel; a gas turbine that produces a fluegas via combusting a second fuel that is different from the first fuel;and a heat exchanger fluidly connected to the primary boiler and to thegas turbine via a first conduit and a second conduit, respectively. Thegenerated steam and the flue gas flow from the primary boiler and thegas turbine via the first conduit and the second conduit, respectively,to the heat exchanger which heats the generated steam via the flue gasto a supercritical steam temperature. In certain embodiments, a firsttemperature of the first conduit is below a critical corrosiontemperature at which contaminants produced by combusting the first fuelcorrode the first conduit and a second temperature of the first conduitis greater than or equal to the critical corrosion temperature. Incertain embodiments, a combined carbon emissions rate of the primaryboiler and the gas turbine is less than a combined carbon emission rateof generating and heating the steam to a supercritical steam temperatureusing one or more boilers that only combust the first fuel. In certainembodiments, the first fuel is at least one of a heavy oil residue, aheavy fuel oil, and a solid fuel. In certain embodiments, the heatexchanger is incorporated into a secondary boiler that heats thegenerated steam. In certain embodiments, the secondary boiler heats thegenerated steam by combusting the second fuel. In certain embodiments,the second fuel is a gas or a combination of a gas blended with at leastone of a liquid fuel or a solid fuel.

Yet still other embodiments provide for a method for providingsupercritical steam. The method includes: generating steam viacombusting a first fuel in a primary boiler fluidly connected to a heatexchanger via a first conduit such that the generated steam flows to theheat exchanger from the primary boiler via the first conduit; andheating the generated steam to a supercritical steam temperature via aflue gas produced by combusting a second fuel in a gas turbine fluidlyconnected to the heat exchanger via a second conduit such that the fluegas flows to the heat exchanger via the second conduit, the second fuelbeing different from the first fuel. In certain embodiments, a firsttemperature of the first conduit is below a critical corrosiontemperature at which contaminants produced by combusting the first fuelcorrode the first conduit and a second temperature of the first conduitis greater than or equal to the critical corrosion temperature. Incertain embodiments, a combined carbon emission rate of the primaryboiler and the gas turbine is less than a combined carbon emission rateof generating and heating the steam to a supercritical steam temperatureusing one or more boilers that only combust the first fuel. In certainembodiments, the first fuel is at least one of a heavy oil residue, aheavy fuel oil, and a solid fuel. In certain embodiments, the heatexchanger is incorporated into a secondary boiler that heats thegenerated steam. In certain embodiments, the secondary boiler heats thegenerated steam by combusting the second fuel. In certain embodiments,the method may further include directing the flue gas into at least oneof the primary boiler or the secondary boiler after the heat exchangerhas heated the generated steam via the flue gas. In certain embodiments,the method may further include generating power via the gas turbineprior to generating steam via combusting the first fuel in the primaryboiler.

Accordingly, as is to be appreciated, by using the second boiler 14 toheat the steam generated by the first boiler 12 to a critical corrosiontemperature, the system 10 can produce supercritical steam without thefirst temperature of the sections of conduit 28, that come into contactwith the contaminants produced via combusting the first fuel 52,exceeding the critical corrosion temperature of the contaminantsproduced by combusting the first fuel 52. Thus, some embodiments of thesystem 10 improve the efficiency of oil-based power plants withoutincreasing the risk of corrosion.

Additionally, some embodiments, where the first fuel 52 is a low-gradeoil such as OHR, allow oil-based power plants to operate undersupercritical steam conditions while taking advantage of abundantlow-grade fuels.

Further, in some embodiments, the second boiler 14 may be smaller thanthe first boiler 12. Thus, in such embodiments, the second boiler 14 maybe disposed within the system 10 close to the steam turbine generator16, thus decreasing the length and cost of the supercritical steamconduit 30. For example, in such embodiments, the length of thesupercritical steam conduit 30 may be on the order of one third of whatit would be with the conventional boiler arrangement without such asecond boiler.

Further still, by combusting a second fuel 60 that produces loweramounts of CO₂ than a first fuel 52, some embodiments of the presentinvention reduce the amount of CO₂ emitted by a power plant. In otherwords, some embodiments of the present invention offload some of thesteam heating duty from a first boiler 12 to a second boiler 14, whereinthe second boiler 14 burns a second fuel 60 that emits less CO₂ than afirst fuel 52 burned by the first boiler 12. Thus, as will beappreciated, in some embodiments of the present invention, the combinedcarbon emissions of the first boiler 12 and the second boiler 14required to generate supercritical steam is lower than the combinedcarbon emissions of using one or more boilers that only burn the firstfuel 52, e.g., a high CO₂ emitting fuel, to generate the same amount ofsuper supercritical steam.

Yet further still, by utilizing gas as the second fuel 60, someembodiments of the present invention provide for higher flue gasvelocities, tighter spacing of conduits, and/or a reduced need forsootblowers.

Moreover, by utilizing a gas turbine generator to heat the generatedsteam, some embodiments provide for an encompassing power plant togenerate electrical power via the gas turbine prior to the completion ofthe primary and/or the secondary boilers.

Additionally, it will be understood embodiments of the present inventionmay be implemented both during construction of a new power plant and/orvia retrofitting of an existing power plant which may, prior to beingretrofitted, generate steam at sub-critical temperatures, e.g., lessthan 565° C. Thus, some embodiments of the present invention may extendthe service lives of existing power plants, and in particular, theservice lives of existing power plants that primarily burn coal.

As is to be appreciated, while the dimensions and types of materialsdescribed herein are intended to define the parameters of the invention,they are by no means limiting and are exemplary embodiments. Many otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, terms such as “first,”“second,” “third,” “upper,” “lower,” “bottom,” “top,” etc. are usedmerely as labels, and are not intended to impose numerical or positionalrequirements on their objects. Further, the limitations of the followingclaims are not written in means-plus-function format are not intended tobe interpreted as such, unless and until such claim limitationsexpressly use the phrase “means for” followed by a statement of functionvoid of further structure.

This written description uses examples to disclose several embodimentsof the invention, including the best mode, and also to enable one ofordinary skill in the art to practice the embodiments of invention,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the invention is definedby the claims, and may include other examples that occur to one ofordinary skill in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty.

Since certain changes may be made in the above-described invention,without departing from the spirit and scope of the invention hereininvolved, it is intended that all of the subject matter of the abovedescription shown in the accompanying drawings shall be interpretedmerely as examples illustrating the inventive concept herein and shallnot be construed as limiting the invention.

What is claimed is:
 1. A system for providing supercritical steamcomprising: a first boiler that generates steam via combusting a firstfuel; and a heat exchanger fluidly connected to the first boiler via aconduit such that the generated steam flows from the first boiler to theheat exchanger; wherein the heat exchanger is disposed in a secondboiler operative to heat the generated steam to a supercritical steamtemperature via combustion of a second fuel that is different from thefirst fuel.
 2. The system of claim 1, wherein the first fuel is at leastone of a heavy oil residue, a heavy fuel oil, and a solid fuel.
 3. Thesystem of claim 1, wherein the second fuel is a gas or a combination ofa gas blended with at least one of a liquid fuel or a solid fuel.
 4. Thesystem of claim 1, wherein the first boiler and the second boiler areeach fluidly connected to a common air source.
 5. The system of claim 1,wherein combustion of the second fuel by the second boiler produces aflue gas, and the second boiler is further fluidly connected to thefirst boiler such that the flue gas flows from the second boiler to thefirst boiler.
 6. The system of claim 1, wherein the system furthercomprises: a steam turbine generator fluidly connected to the secondboiler such that the supercritical steam flows from the second boiler tothe steam turbine generator which consumes the supercritical steam toproduce power.
 7. The system of claim 6, wherein the second boiler formspart of a reheat-cycle-circuit for the steam turbine generator.
 8. Thesystem of claim 1 further comprising: a gas turbine that produces aturbine flue gas via combusting a third fuel that is different from thefirst fuel, wherein the heat exchanger is fluidly connected to the gasturbine so as to heat the generated steam via the turbine flue gas.
 9. Amethod for providing supercritical steam, the method comprising:generating steam via combusting a first fuel in a first boiler fluidlyconnected to a heat exchanger via a conduit such that the generatedsteam flows from the first boiler to the heat exchanger, the heatexchanger disposed in a second boiler; and heating the generated steamto a supercritical steam temperature via the heat exchanger bycombusting in the second boiler a second fuel that is different from thefirst fuel.
 10. The method of claim 9, wherein the first fuel is atleast one of a heavy oil residue, a heavy fuel oil, and a solid fuel.11. The method of claim 9, wherein at least one of the first boiler andthe second boiler is an air-fired boiler or an oxy-fired boiler.
 12. Themethod of claim 9, wherein the second fuel is a gas or a combination ofa gas blended with at least one of a liquid fuel or a solid fuel. 13.The method of claim 9 further comprising: producing power via a steamturbine generator that consumes the supercritical steam.
 14. The methodof claim 13 further comprising: reheating, via the second boiler, steampreviously consumed by the steam turbine generator.
 15. The method ofclaim 9 further comprising: heating the generated steam via the heatexchanger with a flue gas generated by a gas turbine.
 16. A downstreamboiler for providing supercritical steam, the downstream boilercomprising: a combustion chamber configured to generate heat bycombusting a first fuel; and a heat exchanger disposed in the combustionchamber and fluidly connected to an upstream boiler that generates steamby combusting a second fuel that is different from the first fuel;wherein the heat exchanger is operative to heat the generated steam to asupercritical steam temperature via the heat generated by the combustionchamber.
 17. The downstream boiler of claim 16, wherein the first fuelis a gas or a combination of a gas blended with at least one of a liquidfuel or a solid fuel; and the second fuel is at least one of a heavy oilresidue, a heavy fuel oil, and a solid fuel.
 18. The downstream boilerof claim 16, wherein the combustion chamber is configured to be fluidlyconnected to a common air source that is also fluidly connected to theupstream boiler.
 19. The downstream boiler of claim 16 furthercomprising: a flue gas conduit that fluidly connects the combustionchamber to the upstream boiler such that a flue gas produced viacombustion of the first fuel is brought into heating-contact with aneconomizer of the upstream boiler or a feed water line of the upstreamboiler.
 20. The downstream boiler of claim 16, wherein the heatexchanger is operative to heat the generated steam via a turbine fluegas from a gas turbine.